Planning a concrete project? Our concrete calculator helps you estimate exactly how much concrete you need for slabs, driveways, foundations, columns, or any custom shape. Get accurate volume calculations and material breakdowns to avoid ordering too much or too little.
Calculate concrete in cubic yards, cubic feet, or cubic meters, and get instant estimates for cement bags, sand, and gravel needed for your mix.
How to Calculate Concrete Volume
Calculating concrete volume depends on your project shape:
For Slabs and Rectangular Areas
Volume = Length × Width × Thickness
Example: A 20ft × 10ft patio with 4-inch thickness:
- Length: 20 feet
- Width: 10 feet
- Thickness: 4 inches = 0.333 feet
- Volume: 20 × 10 × 0.333 = 66.6 cubic feet = 2.47 cubic yards
For Circular Columns
Volume = π × (Diameter/2)² × Height
Concrete Mix Materials
Standard concrete consists of cement, sand, and gravel mixed in specific ratios:
- 1:2:3 Mix - High strength for foundations and structural elements
- 1:2:4 Mix - Standard mix for slabs and driveways (most common)
- 1:3:5 Mix - Light duty for pathways and light-use areas
Our calculator automatically computes the cement bags, sand volume, and gravel needed based on your selected mix ratio.
Concrete Pouring Tips
- Always add 5-10% wastage to account for spillage and uneven ground
- Order ready-mix concrete for projects over 1 cubic yard
- Mix your own concrete for small jobs under 1 cubic yard
- Standard concrete thickness: 4 inches for slabs, 6 inches for driveways
- One 94-pound bag of Portland cement = 1 cubic foot
Concrete Needed for Common Slab Sizes
Quick reference for standard 4-inch thick slabs with 10% wastage:
| Slab Size | Area (sq ft) | Cubic Yards | 80-lb Bags |
|---|---|---|---|
| 4×4 ft | 16 | 0.22 | 10 |
| 6×6 ft | 36 | 0.49 | 22 |
| 8×10 ft | 80 | 1.10 | 49 |
| 10×10 ft | 100 | 1.37 | 62 |
| 10×12 ft | 120 | 1.65 | 74 |
| 12×12 ft | 144 | 1.98 | 89 |
| 15×15 ft | 225 | 3.09 | 139 |
| 20×20 ft | 400 | 5.49 | 247 |
Based on 4-inch thickness + 10% wastage. For 6-inch slabs, multiply by 1.5.
Frequently Asked Questions
How much concrete do I need for a 10×10 slab?
For a 10×10 foot slab at 4 inches thick, you need about 1.23 cubic yards of concrete. With 10% wastage, order 1.35 cubic yards. That's approximately 50 bags of 80-lb ready-mix concrete, or about half a truckload of ready-mix.
How many bags of concrete do I need?
An 80-lb bag of concrete makes about 0.6 cubic feet. For 1 cubic yard (27 cubic feet), you need about 45 bags of 80-lb mix, or 60 bags of 60-lb mix. For projects over 1 cubic yard, ready-mix delivery is usually more cost-effective.
How thick should a concrete slab be?
Standard thickness is 4 inches for patios, walkways, and shed floors. Use 6 inches for driveways and garage floors. Foundations typically require 8-12 inches. Thicker slabs need more concrete but provide greater load-bearing capacity.
How much does a cubic yard of concrete cost?
Ready-mix concrete costs $120-$150 per cubic yard delivered. Bagged concrete costs about $3-5 per 80-lb bag, working out to roughly $135-$225 per cubic yard. Ready-mix is cheaper for larger projects (2+ cubic yards).
What is the best concrete mix ratio?
The standard mix ratio is 1:2:4 (1 part cement, 2 parts sand, 4 parts gravel) for most projects. Use 1:2:3 for high-strength needs like foundations. Use 1:3:5 for light-duty applications like garden paths.
How long does concrete take to cure?
Concrete reaches about 70% of its full strength in 7 days and full strength (typically 4,000 PSI) in 28 days. Keep it moist for the first 7 days for optimal curing. Avoid heavy loads for at least 7 days.
Should I use ready-mix or bag concrete?
Use bagged concrete for small projects under 1 cubic yard (e.g., fence posts, small pads). For projects over 1 cubic yard, ready-mix delivery is faster, more consistent, and usually cheaper per yard.
How do I calculate concrete for a driveway?
Measure the length, width, and use 6-inch thickness for driveways. For a 20×50 ft driveway at 6 inches: 20 × 50 × 0.5 = 500 cubic feet ÷ 27 = 18.5 cubic yards. Add 10% wastage for 20.4 cubic yards total.